The long term goal of the proposed research is to detect the presence of ischemic heart disease and to evaluate cardiovascular function in children heterozygous for familial hypercholesterolemia with non-invasive studies using maximal exercise testing. The non-invasive studies are exercise-electrocardiogram, indirect blood pressure, heart rate, systolic time interval and work capacity. Early documentation of ischemic heart disease in these children would provide increased rationale for therapeutic intervention with diet or cholestyramine resin or both, designed to normalize total and beta lipoprotein cholesterol. Longitudinal follow-up with non-invasive studies during maximal exercise in such children may provide data relevant to the progression or regression of ischemic heart disease, and the effectiveness of various therapeutic regimens. The study will establish the characteristics of the exercise electrocardiogram in normal children.